An investigation of effect of microwave energy on electrostatic separation of colemanite and ulexite

In this study, an effect of microwave treatment on electrostatic separation of boron minerals namely colemanite and ulexite, obtained from Eti Mines Inc.’s Bigadic Mines in Turkey, was studied in order to determine the changes of electrostatic properties. The X-ray diffraction analyses for the samples showed that colemanite structure was not affected by microwave heat treatment till 900 W power level; however ulexite structure was decomposed after 360 W power level. In addition, TG/DTA results showed that colemanite started to lose its crystal water content at 370.1 (260–427) °C, whereas ulexite lost its crystal water content at 621.9 (60–855) °C. The SEM pictures for the samples also confirmed that microwave treatment affects considerably the particle surfaces in a certain level. The electrostatic separation tests for pure colemanite and ulexite minerals of 1 × 0.5 mm size range at the 10 kV, 18 kV, 20 kV, and 22 kV applied voltages without heating and with heating at 65 °C showed that the colemanite mineral particles behaved as non-conductive up to 18 kV at room temperature and it kept its non-conductivity after heating it at 65 °C and 22 kV. On the other hand, ulexite minerals behaved as conducting at low voltage and room temperature, but it became non-conductive after heating at 65 °C by increasing voltages. These results clearly indicate that separation of these two hydrated borates from each other might be possible for recovery of boron minerals in the industry due to electrostatic properties difference of colemanite and ulexite by heat treatment.

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► Electrostatic separation was performed on pure colemanite and ulexite minerals.
► Colemanite was non-conductive at room temperature.
► After heating colemanite at 65 °C and 22 kV applied voltage, it kept its non-conductivity.
► Ulexite was conductive at low voltage and room temperature.
► After heating ulexite at 65 °C by increasing voltages, it became non-conductive.